The present invention generally relates to welding processes, equipment and materials. More particularly, this invention relates to a welding method and apparatus adapted for filling a groove in an article.
It is often economically beneficial to repair components that have suffered cracks rather than replace them. One such repair technique has been referred to as narrow groove welding. Typically, this technique may require preparation of the component prior to welding. For example, the component may be machined to remove the crack and the region immediately surrounding the cracked, with the result that the component is separated into two or more pieces. Thereafter, a weld buildup technique, for example, a cladding technique, may be used to apply material to the machined surfaces of the component to achieve flat surfaces that can be more readily welded.
Narrow groove welding has become an important technique in the manufacture and repair of thick-walled components, due in part to advantageous features such as high welding speed and weld quality. Methods for performing narrow groove welding have included gas tungsten arc welding (GTAW) techniques (also known as tungsten inert gas (TIG) welding), laser welding, plasma transferred arc (PTA) welding processes and hybrid laser arc welding (HLAW), which can be performed at room and elevated temperatures. For narrow groove welding, these welding techniques use a filler material, typically a ductile filler or a filler whose chemistry closely matches that of the base metal being welded.
The most frequent defect in narrow groove welding is incomplete fusion of the filler material into the walls of the narrow groove. In order to limit the effects of this defect, it is important to maintain uniform and sufficient penetration at both groove walls. Several different approaches have been adopted in attempts to minimize the incomplete wall fusion in narrow groove welding processes. For example, an arc weaving technique has been used wherein a side to side movement along the seam is performed. As a particular example, if a gas metal arc welding technique is used, the electrode may be oscillated by adopting a wire bending technique in which the bending direction is periodically changed. Alternatively, a wire rotating technique can be used that involves rotating an eccentric contact tip. These techniques are effective for penetration at both groove walls. However, wire bending techniques generally require complex systems, the number of oscillations is limited, and the wear resistance of the contact tip is often low. In the case of wire rotating techniques, the minimum root opening is often limited by the need to rotate the whole welding head, and the rotation of the eccentric contact tip may cause the welding head to vibrate, especially in deep groove welding of articles with relatively thick cross-sections.
Additional issues can arise if the component being welded is composed of a highly alloyed metal. Such alloys often have inherently poor weldability and therefore require longer welding operation times in order to achieve fusion with the weld walls. Further, many of these alloys must be preheated prior to welding. For example, CrMoV-base steels, such as those used for components of steam turbine engines, often require a preheat temperature of about 350° F. (about 175° C.) or more. These elevated temperatures may create an environment that is unsuitable for manual welding, in which case narrow groove welding is preferably performed by an automated welding system.
In view of the above, it can be appreciated that there are certain problems, shortcomings or disadvantages associated with prior art narrow groove welding techniques, and it would be desirable if an improved welding technique were developed that was capable of filling a groove in an article to yield a weldment with improved wall fusion.